1. Field of the Invention
The present invention relates generally to the field of fiber optical communications, and in particular to Raman amplification systems and techniques.
2. Background Art
Demand for large transmission capacity has been increasing exponentially due to the rapid spread of Internet services. There is thus an ongoing effort in the fiber optical communications industry to find cost-effective ways to meet this demand.
Currently, network operators deploy optical fiber transport systems employing only one of either the C-band (1530-1565 nm) or L-band (1570-1610 nm). Erbium-doped fiber amplifier (EDFA) technology is typically employed to provide loss compensation. The transmission fiber typically used to implement these systems actually has a spectrum window that is wide enough to transmit signals over a wavelength range encompassing both the C-band and L-band (i.e., 1530-1610 nm), without a guard band (i.e., at 1565-1570 nm). Thus, by employing this combined wavelength range, it would be possible to double transmission capacity over an existing transmission line.
A major obstacle, for deploying an optical transport system in C+L band is the lack of a wide-band optical amplifier that covers the wavelengths ranging from 1530 nm to 1610 nm, without any intermediate guard band (i.e., bandless). Discrete broadband Raman amplifiers will be in high demand in optical networks of this type. However, conventional discrete Raman amplifiers (DRA) will degrade the performance of future WDM polarization-division-multiplexed (PDM) phase-modulated coherent systems. In particular, conventional DRA designs fail to address a number of issues, including nonlinear impairments, associated system performance, and efficiency.